This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Our objective is to develop a way to measure inhibition of fear in rhesus monkeys and humans. In rats we developed a procedure in which one pair of cues (AX+) is paired with an aversive airblast and another pair of cues (BX-) is not paired with an aversive airblast. Under these conditions, rats learned to be afraid of A, not to be afraid of B and the fear of X is some where in the middle. Importantly, when we tested fear to A in the presence of B, we saw that B inhibits fear to A. We set up the AX+, BX- discrimination in humans and tested it in patients with post-traumatic stress disorder. We found that patients with PTSD did not show normal conditioned inhibition which meant we had an objective measure of one of the core symptoms of PTSD, namely the inability to feel safe. We set up the AX+, BX- in rhesus monkeys and found good safety signal learning in three control and one materally separated monkeys. The other two separated monkeys failed to show inhibitory learning. Our lab will continue this work in 34 more monkeys funded by a Challenge grant.